Chemical vapor deposition (CVD) is one of the most widely practiced thin film deposition techniques. Advances in CVD technology have fueled the deployment of many new technologies, including silicon microelectronic processing. One of the key goals for the fabrication of future silicon devices is lower deposition temperatures. These low growth temperatures will limit interlayer and dopant diffusion and facilitate the use of temperature sensitive substances such as polymers or biological materials.
The chemical vapor deposition of SiO2 is ubiquitous in silicon device fabrication. SiO2 CVD films compete effectively with thermal SiO2 that is formed by the reaction of oxygen with the silicon substrate at 900-1200 K. SiO2 CVD is performed at various temperatures that can be significantly lower than the required temperatures for thermal SiO2 growth. At high temperatures of xcx9c1200 K, excellent SiO2 films with properties close to thermal SiO2 can be grown using the reaction SiH2Cl2+2NOxe2x86x92SiO2+2N2+2HCl. At medium temperatures of xcx9c900-1000 K, very reasonable SiO2 dielectric films are deposited using tetraethyl orthosilicate (TEOS) decomposition. Several earlier investigations have reported the kinetics of SiO2 CVD using SiCl4 and H2O. These studies observed efficient SiO2 CVD only at temperatures greater than 900 K. At fairly low temperatures of xcx9c500-700 K, SiO2 films with a lower density than thermal SiO2 can be deposited using the reaction SiH4+O2xe2x86x92SiO2+2H2O.
SiO2 deposition at temperatures as low as room temperature has been the focus of recent research. Plasma processing is often used to lower film deposition temperatures. However, the drawbacks to plasma processing are particle contamination, surface damage from the energetic plasma species and high interface defect density. The use of novel molecular precursors has also been explored for low temperature SiO2 growth. However, these precursors are usually expensive, and the SiO2 films deposited with these precursors have not been device quality.
Amine catalysts have been used for the attachment of chlorosilanes and organosilanes to silica surfaces. See C. P. Tripp and M. L. Hair, J. Phys. Chem. 97, 5693 (1993) and J. P. Blitz et al., J. Amer. Chem. Soc. 109, 7141 (1987). The use of a catalyst has also recently been reported for SiO2 atomic layer deposition (ALD) using sequential surface reactions. These SiO2 ALD investigations used either pyridine (C5H5N) or ammonia (NH3) as the catalyst during sequential exposures to SiCl4 and H2O. See J. W. Klaus, O. Sneh, A. W. Ott and S. M. George, Surface Review and Letters 6, 435 (1999) and J. W. Klaus, O. Sneh, A. W. Ott and S. M. George, Science 278, 1934 (1997). These previous studies demonstrated that Lewis base molecules can catalyze SiO2 ALD at room temperature. Recent ab initio theoretical calculations have confirmed the catalytic effect of NH3 on the SiCl4 and H2O half-reactions occurring during SiO2 ALD. Y. Okamoto, J. Phys. Chem. B 103, 11074 (1999).